Chromium plating



Nov. 12, 1935.

R. SCHNEIDEWIND CHROMIUM PLATING Filed June 13, 1934 E w W u. IInOv P i T D 12* R m 05 B R U C m1 HYDROQUINONE Patented 'Nov. 12, 1935 UNITED STATES PATENT OFFICE 2,020,332 CHBOMIUM rm'rmo Richard Schneidewind, Ann Arbor, men. v Application June 13, 1934, Serial No. 730,421

Claims. This invention relates to a method for increas ing the throwing power and utility of a chroplating solution containing from 100 to 450 grams of CIOa and from 0.5 to 6.2 grams of S04. The data in this applicationdefinitely' proves that butler agents such as boric acid and the like increase the upper limit of current density for plating articles with a bright chromium deposit.

I have now found that the incorporation of quinones, which are readily oxidized and reduced the throwing power of a chromic acid-plating bath by incorporating a quinone therein.

Another object of this invention is to provide a method for increasing the throwing power of chromic acid plating baths by incorporating quinones therein which are readily oxidized and reduced under the influence of electrolysis without interfering with the plating operation.

A further object of this invention is to provide a chromic acid plating bath of increased throw- 1o ing power by incorporating hydroquinone therein. Other and further objects of this invention will be apparent to those skilled in the art from the following specification and annexed sheet of 15 drawing which forms a part of this specification.

On the drawing: Figure 1 is a chart showing the effect of varying amounts of hydroquinone on the upper and lower limiting current densities in chromium plating baths containing 250 grams per liter of CrOs and about 2.5 grams per liter of. sulphate radicals ($04). The curves were plotted from the following data:

Temp. 45 C. Sulphate ratio, CrOJJBOu- CKO==25O g/1,

Plating range Throwing power 30 Hydroqulnone grams per liter A B g Lower limit Upper limit amp/sq. it. ampJsq. it.

205 0.? 33 g gs as 0.2 25 200 2.0 0. 25 20 200 10.0 0.5 4 11 205 12.1 1.0 20 200 10.3 2.0 20 200 10.0 5.0 20 6.72 40 under the influence of electrolysis, into a chro- Figure 2 is a combined chart showing the effect mic acidplating bath decreases the necessary of the change of sulphate ratio current density heretofore required for the production of bright plating. Ihave found that (3:0,) 45 quinones suchas benzoquinone, hydroquinone, so

naphthaquinone, anthraquinone and the like are operable for this purpose.

It is therefore an object of thisinvention to provide a chromium plating bath having increased throwing power especially in the lower ranges of current density used in the electrodeposition of chromium on metals for the production of bright plated surfaces thereon.

Another object of this invention is to increase on the throwing power of chromic acid plating baths containing no hydroquinone and containing 0.5 grams perliter of hydroquinone. Curves 50 1 and 3 were obtained from plating operations carried out at 45 C. Curve 2 was obtained from. data in plating operations carried out at 25 C. while curve 4 was obtained from data in plating operations eflected at 60 0. 55

The data from which the curves were plotted in chart 2 is indicated in the following table:

treme tips also showed grayness. It should be appreciated that while only the upper and lower Plating range Te'nipercro Throwing a um. I power Hydroqulnone /1 W A B 2 Lower limit Upper limit amp/sq. it. smpi/sq. it.

The chromic acid plating bath used in each instance contained 250 grams per liter of chromic acid (QrOa).

Since it is always desirable to prepare a plating bath which can be used throughout a wide range of current densities it will be readily appreciated that the presence of a quinone such as hydroquinone is advantageous because, as shown in Figure l, the quinone considerably lowers the lower limiting current density.- The presence of even minute quantities of hydroquinone, for

example 0.1 gram per literreduces the lower limit of the plating range ironi'about 65 amperes per square root to about amperes per square root. .The upper limiting current density is not materially ailected although chart 1 shows that the presence of considerable amounts of hydroquinone, lie. 5 grams or more per liter, tends to lower the upp r limit.

The throwing power or the plating bath as indicated'by the above tables is determined by -dividing the upper limiting current density by 4 the lower limiting current density;

The 'currentdensities were determined unii'ormlyaccording to the iollowing procedure. A cylindrical steel tank three inches in diameter and seven inches deep was connected electrically new 0. (140'I".). "The strips were plated stvarying current densities and the quality of the deposit on'the strips was examined in diil'used light. The time of plating was 120 seconds for the higher current densities and 180 seconds for the lower current densities.

A satisfactory plate was one which covered the specimen copper strip completely and brightlvwithnotraceotdullnessorburning atthe tips. The upper and lower limits-oi the current densities were thus determined and it was also iound that u; some instances bright plating was obtained below the tabulated limiting current densities. However these data were rejected since traces of copper could be seen at the center citheupperedgeotthespecimen. Thee:-

sasss cease eases cease ss =s ss as' saaEE asses seems 22255 ENENN vpgpe fie??? PP??? limiting current densities are correlated in the above tables it was necessary to carry out from 5 to 15 separate tests to determine'each upper "creases the throwing power of chromic acid plating baths that the sulphate ratio may be varied considerably from this amount without approaching the weaker throwing power oi" a chromic acid plating bath which does not contain.

a quinone. 'Thus at 45 C. satisfactory bright plating deposits were obtained with a sulphate quinone was present in the bath.

Since hydroquinone, as indicated in the accompanying charts, materiaily decreases the lower limiting current density without substan-.

tially ail'ecting the upper limiting current density, the presence of a quinone is highly desirable in plating operations where current density must be kept at a minimum. The lower current density,

it desired, may be applied by "striking" i. e. ap-' plying a higher current for a short period oi time, 4

tor example, about 10 seconds. It a plating bath found that plating -,will take place at as low as 20 amperes per square root at 45 0. Thus the hydroquinone seems to function as a depolariser permitting deposition or chromium at approxipossible in abratio as high as 300. The bath had a throwing 45,

' power 01- 5.58 as compared with 2.32 when no 204. UHtMISlHY, tLtUlHIUAL & WAVE ENERGY.

aiuiiici This action of course may explain that the quinones act as depolarizers but I do not desire to be limited by any theory since it is possible that the presence of the substance has an entirely different chemical effect which is not at the present time understood.

I have found that the presence of one-half gram per liter of anthraquinone in a standard Sargent plating bath at 45 increases the throwing power from 3.17 to 3.72. The presence of one-half gram per liter of naphthaquinone increases the throwing power to 4.5. If one gram per liter of naphthaquinone is used in the plating bath, the throwing power is increased further to 6.62. The presence of 0.5 gram per liter of benzequinone in the above mentioned plating bath increases the throwing power to 8.06.

From the above it is evident that a quinone has a decided beneficial effect upon chromic acid plating baths especially when the plating operation is carried out at low current densities. The quinone is apparently most beneficial in plating operations for the deposition of chromium directly on a copper surface. This copper surface need only be of minute thickness.

I am aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

Having now described my invention, what I claim is:

1. The method of increasing the throwing powe of chromium plating baths which comprises incorporating a quinone into said baths.

2. The method of increasing the throwing power of chromic acid plating baths having a sulphate ratio within the range of 50 to 300 which comprises incorporating small amounts of a quinone in the baths.

3. The method of increasing the throwing power of chromium plating baths containing about 250 grams per liter of chromic acid (C103) and about 2.5 grams per liter of sulphate radicals (S04) which comprises incorporating in said baths an amount of a quinone equivalent to .05 to 5 grams per liter of hydroquinone.

4. The method of increasing the throwing power of standard chromic acid plating baths which comprises incorporating therein a depolarizer selected from the group consisting of benzoquinone, hydroquinone, anthraquinone, and naphthaquinone.

5. The method of lowering the lower limiting current density in chromium plating operations 5 which comprises dissolving hydroquinone into the chromic acid plating bath.

6. The method of chromium plating which comprises depositing chromium on a copper surface from a chromic acid plating bath contain- 10 ing small amounts of a quinone at current densities equivalent to below amperes per square feet at 45 C.

7. The method of chromium plating which comprises depositing chromium on a copper sur- 15 face from a chromic acid plating bath containing about 250 grams per liter of chromic acid (CrOs). about 2.5 grams per liter of sulphate radicals (S04) and from 0.1 to 5 grams per liter of hydroquinone at current densities between 20 and 200 20 amperes per square feet at 45 C.

8. As a. new composition, a plating bath containing chromic acid, sulphate radicals and small amounts of a quinone.

9. As a new composition, a plating bath con- 5 taining chromic acid and sulphate radicals, the ratio CIO3/SO4 being from 50 to 300, and containing from 0.1 to 5 grams per liter of a quinone.

10. The process of increasing the throwing power of chromic acid plating baths which com- 30 prises incorporating into said baths small amounts of anthraquinone.

11. The process 01' increasing the throwing power of chromic acid plating baths which comprises incorporating into said baths small 5 amounts of naphfhaquinone.

12. As a new composition, a plating bath containing chromic acid, sulphate radicals and small amounts of hydroquinone.

13. As a new composition, a plating bath con- 40 taining chromic acid, sulphate radicals and small amounts of anthraquinone.

14. As a new composition, a plating bath containing chromic acid, sulphate radicals and small amounts of naphthaquinone. 45

15. As a new composition, a plating bath containing chromic acid and sulphate radicals, the ratio CiO3/SO4 being from 50 to 300, and containing from 0.1 to 5 grams per liter of hydroquinone.

RICHARD SCHNEIDEWIND. 5o 

